This invention relates to piezoelectric pressure pickups for fuel injection lines in internal combustion engines in general and more particularly to an improved pickup which is easier to install than those previously used in the art.
In particular for the diagnosis of Diesel engines, the exact determination of the beginning of injection is of as great an importance as is the determination of the instance of ignition in externally fired internal combustion engines. This is true whether it is done to correlate events in the individual cylinders with the correct cylinder or to correlate the injection process of the individual cylinders with a given piston position of the respective cylinder.
A diagnostic device for Diesel engines is described in U.S. Pat. No. 3,503,255. In the device disclosed therein, quartz pickups are used for measuring the pressures in injection lines. Other than indicating that such pressure pickups are used, this patent teaches nothing further as to the nature of the pressure pickups.
In German Offenlegungsschrift No. 21 10 107, a device for analyzing a fuel flow in which a sensor for the fuel flow is built into the fuel line is described. A similar device for measuring pressures in injection lines is described in German Offenlegungsschrift No. 21 43 476. In the device described therein an appropriate sensor is inserted into the fuel pressure system as a separate adaptor after the fuel line is unscrewed. These known pressure sensors require a considerable amount of time for installation when diagnosis is required. Furthermore, they change the cross section and/or the length of the fuel line, factors which are important for the shape of the pressure rise and therefore for the instant of the injection.
Thus, the need for an improved pressure pickup for use in measuring the pressure in injection lines in an internal combustion engine is evident.